1. Field of the Invention
The present invention relates to a high-frequency module that transmits and receives multiple communication signals via a common antenna.
2. Description of the Related Art
Various high-frequency modules that transmit and receive multiple communication signals using different frequency bands with common antennas have been proposed. For example, a high-frequency module disclosed in Japanese Unexamined Patent Application Publication No. 2005-64778 includes a switch integrated circuit (IC) and multiple duplexers. An antenna is connected to a common terminal in the switch IC and the respective duplexers are connected to individual terminals in the switch IC.
The high-frequency module disclosed in Japanese Unexamined Patent Application Publication No. 2005-64778 has, for example, a circuit configuration shown in FIG. 1. FIG. 1 is a diagram showing the circuit configuration of a high-frequency module 10P. Only a reception system circuit will be simply described here. Referring to FIG. 1, a switch IC 11 includes a common terminal PIC0 and individual terminals PIC11 to PIC16.
In reception of a Global System for Mobile Communication 850 (GSM850) communication signal and a GSM900 communication signal, the switch IC 11 connects the common terminal PIC0 to the individual terminal PIC13. In this case, the GSM850 communication signal and the GSM900 communication signal received via an antenna ANT are transmitted to the individual terminal PIC13.
A surface acoustic wave (SAW) duplexer SDP12 including SAW filters SAW1 and SAW2 is connected to the individual terminal PIC13. A phase circuit including a serially connected inductor L11 and a capacitor C11 grounding one end of the inductor L11 is connected between the individual terminal PIC13 and the SAW filter SAW1. A phase circuit including a serially connected capacitor C21 and an inductor L21 grounding one end of the capacitor C21 is connected between the individual terminal PIC13 and the SAW filter SAW2. In these phase circuits, the element values are determined so that the SAW filter SAW2 side is open (the reflection coefficient is maximized) for the GSM850 communication signal and the SAW filter SAW1 side is open (the reflection coefficient is maximized) for the GSM900 communication signal. The element values are determined in the above manner to ensure a certain level or higher of isolation between the SAW filters SAW1 and SAW2.
Similarly, when receiving a GSM1800 communication signal and a GSM1900 communication signal, the switch IC 11 connects the common terminal PIC0 to the individual terminal PIC14. In this case, the GSM1800 communication signal and the GSM1900 communication signal received via the antenna ANT are transmitted to the individual terminal PIC14.
A SAW duplexer SDP34 including SAW filters SAW3 and SAW4 is connected to the individual terminal PIC14. A phase circuit including a serially connected inductor L31 and a capacitor C31 grounding one end of the inductor L31 is connected between the individual terminal PIC14 and the SAW filter SAW3. A phase circuit including a serially connected capacitor C41 and an inductor L41 grounding one end of the capacitor C41 is connected between the individual terminal PIC14 and the SAW filter SAW4. In these phase circuits, the element values are determined so that the SAW filter SAW4 side is open (the reflection coefficient is maximized) for the GSM1800 communication signal and the SAW filter SAW3 side is open (the reflection coefficient is maximized) for the GSM1900 communication signal. The element values are determined in the above manner to ensure a certain level or higher of isolation between the SAW filters SAW3 and SAW4.
However, in the high-frequency module 10P described above, the pass bands of the SAW filters composing the SAW duplexer connected to one individual terminal in the switch IC 11 are close to each other. In other words, the frequency bands of the communication signals passing through the respective SAW filters are close to each other.
Accordingly, there are cases where it is not possible to set the frequency bands so as to achieve transmission characteristics having sufficiently low loss for the frequency band of one communication signal, among the two communication signals output from each individual terminal, and reflection characteristics sufficient for the frequency band of the remaining communication signal.